Scientists build theory on human face recognition

LONDON, July 6 (Reuters) Monkeys recognise each other by comparing faces to an average stored in their brains, not by memorising what every individual looks like, scientists have said.

And that probably goes for people, too, explaining how faces can be recognised in a fraction of a second, they said yesterday.

The scientists found in their study that a monkey's brain did not keep track of different parts of a face, storing and then accessing the information to recognise others.

Instead it keeps a statistical average of the faces it has seen and uses it as a basis for comparison.

''When it sees a new face it compares it to this average and then it remarks upon the differences ... and that is how the face is seen,'' said David Leopold, of the National Institute of Mental Health in Bethesda, Maryland.

''It elucidates how it is possible that you can so quickly and effortlessly, in just a few hundred milliseconds, recognise faces,'' he added.

Leopold and his colleagues pinpointed the recognition system while studying neurons in an area of the brain called the inferotemporal cortex in two macaque monkeys which had been trained to recognise computer-generated human faces.

They monitored single neurons to understand how groups of the brain cells work together to recognise faces.

''What we found is that the neurons in this part of the monkey's brain respond in a way that is extremely sensitive to the small differences in information between faces of different identities,'' said Leopold, who reported the research in the science journal Nature.

The activity of the neurons was monitored as the monkeys were shown an average face of a person and as it was artificially morphed the full identity.

''The main finding was a striking tendency for neurons to show tuning that appeared centred about the average face,'' Leopold said in the journal.

In psychological tests, humans identify faces in much the same way as monkeys so the researchers believe this aspect of the visual recognition system is similar in both species.